What layer of the Open System Interconnect model defines the electrical, mechanical, procedural, and functional specifications for links between communicating network systems?

The Physical layer of the Open System Interconnection (OSI) model is responsible for defining the electrical, mechanical, procedural, and functional specifications for links between communicating network systems. This layer encompasses all the hardware involved in the transmission of data over a network, including cables, switches, and other devices that transmit raw bit streams. It specifies aspects such as voltage levels, timing of voltage changes, and physical data rates, ensuring that data transmitted over various physical mediums (like copper, fiber optics, or wireless) maintains integrity and usability across different devices and platforms.

This layer serves as the foundation for the other layers in the OSI model, enabling reliable communication by establishing the basic means of transferring data. By defining these specifications, the Physical layer ensures that devices from different manufacturers can connect and communicate effectively, which is critical for establishing successful network communication.

In contrast, the Data Link layer is focused more on node-to-node data transfer and error handling, the Network layer manages routing and forwarding of data packets, and the Transport layer is primarily concerned with end-to-end communication and data integrity between applications. Each layer builds upon the capabilities of the Physical layer but does not define the physical characteristics required for transmitting data.